1. Field of the Invention
The present invention relates to a hemoglobin composition, particularly relates to a modified hemoglobin composition, which is capable of dynamically regulating the efficiency of oxygen release.
2. The Prior Arts
The hemoglobin (Hb) is a primary carrier for transporting oxygen in the blood. The hemoglobin contained in human body is a kind of tetramer consisting of two  subunits and two β subunits, which are non-covalently bonded. The molecular weight of each subunit, consisting of one α chain or β chain together with one heme, is about 16,000 daltons. The heme molecule comprises one bivalent ferrous ion for either associating with oxygen molecules, or releasing oxygen molecules to cells under appropriate circumstances.
Although free hemoglobin has the function of carrying oxygen molecules, it still couldn't be a substitute as blood and directly put into human body. The reason lies on that free hemoglobin in a low concentration easily tends to dissociate from tetramer into dimers in human body, where the hemoglobin dimers will conjugate with haptoglobin in blood and then be degraded in liver, and hence decreasing the concentration of haptoglobin. However, when under higher concentration of free hemoglobin, it is not only the above-mentioned metabolism problems arisen, the excessive amount of hemoglobin dimers wouldn't be metabolized thoroughly by liver, and under this circumstance, part of the hemoglobin dimers will be transferred to kidney for metabolism, and hence easily result in the renal dysfunction as well, or even cause renal tubular obstruction due to the passage of hemoglobin dimers through renal corpuscles.
On the other hand, when unmodified hemoglobin has been transfused into human body, it will be spread into the spaces between endothelium and smooth muscle cells and react with nitric oxide therein, and consequently result in the decrease of the concentration of nitric oxide which is capable of activating the soluble guanylyl cyclase (sGC) contained in smooth muscle cells, and thus can't afford sufficient amount of cyclic GMP (cGMP) during metabolic processes. As a result of the shortage of cGMP, the concentration of calcium ions will be unable to be regulated via ion channels and hence accumulated in cells instead. Furthermore, the high concentration calcium ions stocked in cells will also cause the blood vessel contraction as well as result in high blood pressure consequently.
With regard to the resolutions to overcome the critical physiological defects above-mentioned of the hemoglobin with unmodified conformation, while referring to known skills, it is found that most of them are to crosslink either among peptide chains of each subunit or among hemoglobin molecules, or try the method to prevent the dissociation from hemoglobin tetramers. Among them, the familiar inventions for hemoglobin modification, such as U.S. Pat. No. 4,670,417, No. 5,234,903, No. 5,312,808 and No. 6,017,943, polyethylene glycol (PEG) in which are utilized to crossbridge hemoglobin molecules. In addition, some inventions are focusing on the improved skills by utilizing dextran, hydroxyethyl starch, inulin or polyvinylpyrrolidone for hemoglobin crosslinkage, or even encapsulating the hemoglobin into the liposome. Those inventions described above are either capable of crosslinking or aggregating the hemoglobin molecules in order to obtain larger molecules, so that it is applicable to prevent hemoglobin tetramer from being dissociated into dimers and thus won't have side effects of renal function, high blood pressure etc. resulted due to the dissociation from tetramers into dimers as well as spread into spaces between endothelium and smooth muscle cells. Besides, owing to the larger molecular weight and tetramer conformation, the modified hemoglobin would have some advantages such as retarding the decomposition reaction by the protease, and prevent rapid clearance by human body at the same time.
Whereas the prior inventions utilized the methods of crosslinking among hemoglobin molecules or crosslinking peptide chains within each hemoglobin molecule so as to form a larger and more stable molecule to maintain a conformation of hemoglobin tetramer or hemoglobin polymer in order to eliminate side effects of renal function, high blood pressure, they did affect the original conformation of hemoglobin after crosslinking process and then further affect the efficiency of oxygen affinity as well as cooperative effect under normal condition, and thus dramatically decrease both the efficiency of oxygen transportation and providing consequently. On the other hand, the prior hemoglobin solution only has the hemoglobin molecules, excluding other regulatory factors, for instance, 2,3-diphosphogylcerate (2,3-DPG), which is able to bind to the oxygen-carrying hemoglobin and transform which into T state stably. Therefore, if this kind of hemoglobin solution is being used upon blood transfusion, the hemoglobin herein won't be able to release oxygen appropriately while under some circumstance, and thus be impossible to meet the requirement of appropriate efficiency of oxygen supply while under regular circumstance.